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Sampling the atmosphere, ten miles high

Laura Pan, NCAR's Atmospheric Chemistry Division

Laura "Liwen" Pan (Photo by Carlye Calvin, UCAR.)

Laura Pan describes herself as an "accidental" scientist. She never intentionally set out to pursue a science career. Rather, she began with an interest in theoretical physics and found herself drawn along as adventures unfolded, first in remote sensing and more recently in high-altitude research flights.

Her pursuit of knowledge and understanding, however, is anything but accidental. For while Laura may have a doctorate in physics, what she doesn't have—a high school diploma—is equally revealing.

When Laura was in fourth grade, the Cultural Revolution swept through her native China and schools closed amidst political unrest. Laura, who loved to learn, was crushed. As she describes in a 1993 essay, The Two Libraries that Changed My Life, over the next 12 years she first slept in a library and was then employed by a school that gave her access to one. During this time, she taught herself math, English, literature, philosophy, and more, submitting to a rigorous self-education that would open doors later in life and eventually lead her to NCAR.

Today, Laura studies atmospheric dynamics, or motions in the atmosphere associated with weather and climate. In particular, she focuses on the upper troposphere and lower stratosphere. The troposphere is the lowest layer of Earth's atmosphere, extending from the surface up about 5 to 9 miles (8-14 kilometers), where it merges into the atmosphere's next layer, the stratosphere. The thin buffer zone between them is called the tropopause.

The dynamics, chemistry, and clouds of the upper troposphere and lower stratosphere are connected. Water vapor and ozone are exchanged between the two layers via the tropopause. These transport process in turn have an important impact on climate.

Through an NCAR initiative called UTLS (Upper Troposphere, Lower Stratosphere), Laura seeks to understand the chemical behavior of the tropopause and how the tropopause separates the layers above it and below. One of her main activities is planning missions for the new NSF/NCAR G-V aircraft. The nation's most advanced research aircraft, the G-V can fly at altitudes up to about 10 miles (15 kilometers), making it the ideal platform for scientists to study the tropopause.

In 2005, Laura was the principal investigator and a mission scientist for the G-V's first flight demonstrating its research capabilities. She led an experiment called START (Stratosphere-Troposphere Analyses of Regional Transport), which involved proposing instruments for deployment on the G-V, designing the flight plan, flying aboard the plane, and later analyzing the chemicals measured in the troposphere and stratosphere.

She also participated in the aircraft's next mission, T-REX (Terrain-induced Rotor Experiment), which had a UTLS component to study the effects of mountain winds on chemical transport between the troposphere and stratosphere.

"I feel very fortunate to be involved in the use of the G-V, and I've gotten to work with a lot of good people," Laura says.

This three-dimensional figure illustrates the flight tracks of the NSF/NCAR G-V (also known as HIAPER) during the aircraft's first flight to demonstrate its research capabilities, the START mission (Stratosphere-Troposphere Analyses of Regional Transport). The gold surface represents the fold of the tropopause that was sampled during the flight, which Laura planned and directed with help from G-V chief scientist Al Cooper. Colors on the flight track within the fold indicate ozone values measured directly by instruments aboard the aircraft. The stratospheric air mass has high values of ozone (shown in yellow), greater than 200 parts per billion by volume (ppbv). The tropospheric air has low values of ozone (shown in light blue), less than 60 ppbv. The tropopause region has transitional values (dark blue and red). Click here or on the image to enlarge. (Image by Laura Pan, NCAR, in collaboration with Kenneth Bowman of Texas A&M University.)

The fact that her work sends her into the sky has been a pleasant surprise. "When I started working on the UTLS project, I didn't ever think that I was going to fly, so it took a bit of adjustment," she says. "It's really interesting and you learn so much."

Laura appreciates that her research has relevance to society. "You feel you have a deeper understanding of the world and you never get bored because you learn something new every day," she says, adding that the atmospheric sciences are particularly relevant in this age of environmental crisis. "I feel I'm being a part of human decision-making."

While she's constantly learning new things, she's simultaneously discovering everything she doesn't know. "You're always working at the margins of your ability and knowledge," she says. "There's no end. You'll never be satisfied because you have more to do."

Growing up, Laura obviously loved to study, considering her self-education at the library. But she never imagined she would be a scientist some day, particularly when she was denied the opportunity to attend high school.

When the Cultural Revolution ended in 1977, China held a nationwide college entrance exam, open to everyone regardless of whether they had attended high school. Laura had unknowingly taught herself far more math than was required of high school students at the time. She got a perfect score.

When it came time to choose a major, she reflected on experiences endured by her parents, both researchers of Chinese history during the Cultural Revolution. She decided to study math and science at the university. "I watched as researchers in social studies could not do objective research because everything depended on the political leaders of the country," she recalls. "I wanted to avoid that."

At the university, she discovered a passion for physics. "I knew nothing about physics when I started, but was only trying to avoid the political constraints my parents experienced. Then I learned about Einstein and other intellectual giants. I was enchanted by physics soon after."

During Laura's junior year, a group of U.S. universities launched a scholarship program for Chinese graduate students. Her self-education in the libraries once again paid off when she was able to take the required physics test in English, something very few Chinese students at that time could do. She was awarded a scholarship to Johns Hopkins University.

At Hopkins, Laura completed a doctorate in theoretical quantum optics, followed by postdoctoral research at the National Institute of Standards and Technology. About this time, she found herself grappling with how to balance her career with raising a family. While working on a NASA project on ozone, she realized that the atmospheric sciences would offer her a broader array of career tracks than pure physics.

So in 1992, Laura came to NCAR to support the development of MOPITT (Measurements of Pollution in the Troposphere), an instrument that now flies on a NASA spacecraft, measuring the global distributions of carbon monoxide and methane in the troposphere.

"I was trained for and had success in my early career in theoretical quantum optics, a field very different from what I am doing right now," she says. "Switching to atmospheric research and becoming a scientist in this new field at an institution like NCAR was no small deal. But hard decisions often need to be made by scientists with families and dual careers, certainly in my case."

Later, she made another major transition, from remote sensing and satellite data research to her current role as a research flight scientist for UTLS.

"Part of being an accidental scientist requires you to be adventurous, which in turn requires you to be willing to start from scratch, and be prepared to fail," she says.

Currently, Laura's preparing for another START experiment planned for 2008, during which her research team will sample the tropopause with more advanced instruments than those available for the 2005 mission.

Laura says she has a strong personal drive to succeed as a scientist, but she also credits the people and work environment around her. "Without good mentors and a strong support structure, I wouldn't have lasted this long," she notes. "There are things that come from within, but you also need opportunities from the outside, and a bit of luck."